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January 7, 2011

X-Rays Reveal Ammonites Dined On Plankton

by Sam Savage

Using a special form of X-ray technology, French and American researchers have managed to discern the diets of the extinct, squid-like creatures known as ammonites.

The experts used the European Synchrotron Radiation Facility (ESRF) in Grenoble to analyze ammonite fossils using synchrotron X-rays. They discovered that the ancient creatures, which died out more than 65 million years ago and are related to the squid and the octopus, ate plankton.

According to an ESRF press release dated January 6, "The team of researchers, led by Isabelle Kruta"¦ used the ESRF to perform X-ray scans of exceptional quality of Baculites fossils found on AMNH [American Museum of Natural History] expeditions to the Great Plains in the United States. Results suggests that the large group of ammonites to which Baculites belongs, had jaws and radula (a kind of tongue covered with teeth) adapted for eating small prey floating in the water."

Images of the X-rays have been published in the journal Science, and according to BBC News Science Correspondent Jonathan Amos, they "reveal the mouthparts of three ammonite specimens" which were discovered in South Dakota. The researchers have also created 3D replicas of the jaws and radula, Amos said in an article published Thursday.

"I was astonished when I saw the teeth for the first time, and when I found the tiny plankton in the mouth," Kruta, who was lead author of the study and represents Museum National dÃ´Histoire Naturelle in Paris, said in a statement. "For the first time we were able to observe the delicacy of these exceptionally well preserved structures and use high quality details to obtain information on the ecology of these enigmatic animals."

"When you take into consideration the large lower jaws of ammonites in combination with this new information about their teeth, you realize that these animals must have been feeding in a different way from modern carrion-eating Nautilus," added Neil Landman of the American Museum of Natural History. "Ammonites have a surprisingly large lower jaw with slender teeth, but"¦ the bigger mouth facilitates feeding on smaller prey."

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Image 1: These are fossils of ammonites, including Baculites (the long straight-shell), from Upper Cretaceous deposits in South Dakota. Credit: S. Thurston

Image 2: 3-D reconstruction of the radula (tongue-like anatomical structure of mollusks for feeding) of a Baculites fossil. Teeth are depicted in yellow and the fragments of the fossil's last meal, caught between the jaws, in blue (for a crustacean) and pink (for a snail), respectively. Credit: I. Kruta/MNHN